from ..target.ATarget import ATarget
from ..SpectralQty import SpectralQty
import astropy.units as u
from astropy.modeling.models import BlackBody
from astropy.constants import c, k_B
from ...lib.logger import logger
from ..Entry import Entry
from typing import Union
import numpy as np
[docs]class BlackBodyTarget(ATarget):
"""
This class models the spectral flux density of a star of given magnitude using as black body radiator
"""
# Bands from Handbook of Space Astronomy and Astrophysics p. 139
_band = dict(U=dict(wl=365 * u.nm, sfd=4.27e-11 * u.W / (u.m ** 2 * u.nm)),
B=dict(wl=440 * u.nm, sfd=6.61e-11 * u.W / (u.m ** 2 * u.nm)),
V=dict(wl=550 * u.nm, sfd=3.64e-11 * u.W / (u.m ** 2 * u.nm)),
R=dict(wl=700 * u.nm, sfd=1.74e-11 * u.W / (u.m ** 2 * u.nm)),
I=dict(wl=900 * u.nm, sfd=8.32e-12 * u.W / (u.m ** 2 * u.nm)),
J=dict(wl=1250 * u.nm, sfd=3.18e-12 * u.W / (u.m ** 2 * u.nm)),
H=dict(wl=1650 * u.nm, sfd=1.18e-12 * u.W / (u.m ** 2 * u.nm)),
K=dict(wl=2200 * u.nm, sfd=4.17e-13 * u.W / (u.m ** 2 * u.nm)),
L=dict(wl=3600 * u.nm, sfd=6.23e-14 * u.W / (u.m ** 2 * u.nm)),
M=dict(wl=4800 * u.nm, sfd=2.07e-14 * u.W / (u.m ** 2 * u.nm)),
N=dict(wl=10200 * u.nm, sfd=1.23e-15 * u.W / (u.m ** 2 * u.nm)))
@u.quantity_input(wl_bins='length', temp=[u.Kelvin, u.Celsius], mag=[u.mag, u.mag / u.sr])
def __init__(self, wl_bins: u.Quantity, temp: u.Quantity = 5778 * u.K, mag: u.Quantity = None,
band: str = "V", law: str = "Planck"):
"""
Initialize a new black body point source
Parameters
----------
wl_bins : length-Quantity
Wavelengths used for binning
temp : Quantity in Kelvin / Celsius
Temperature of the black body
mag : Quantity in mag or mag / sr
Desired apparent magnitude of the black body source. If the magnitude is given in mag / sr or an equivalent
unit, an extended source will be assumed.
band : str
Band used for fitting the planck curve to a star of 0th magnitude. Can be one of [U, B, V, R, I, J, H, K].
law : str
Which law to use for the calculation of the flux values. Can be either 'Planck' for using Planck's law or
'RJ' to use the Rayleigh-Jeans approximation.
Returns
-------
"""
if band.upper() not in self._band.keys():
logger.error("Band has to be one of '[" + ", ".join(list(self._band.keys())) + "]'")
# Create blackbody model with given temperature
bb = None
if law.lower() == "planck":
bb = BlackBody(temperature=temp, scale=1 * u.W / (u.m ** 2 * u.nm * u.sr))
elif law.upper() == "RJ":
bb = self.__rayleigh_jeans_factory(temp)
else:
logger.error("Unknown law '" + law + "' for target type BlackBody.")
if mag is not None:
# Calculate the correction factor for a star of 0th magnitude using the spectral flux density
# for the central wavelength of the given band
if mag.unit.is_equivalent(u.mag / u.sr):
solid_angle_unit = (u.mag / mag.unit)
mag = mag * solid_angle_unit
factor = self._band[band.upper()]["sfd"] / (bb(self._band[band.upper()]["wl"]) * (
solid_angle_unit.to(u.sr) * u.sr))
else:
factor = self._band[band.upper()]["sfd"] / (bb(self._band[band.upper()]["wl"]) * u.sr) * u.sr
# Calculate spectral flux density for the given wavelengths and scale it for a star of the given magnitude
sfd = bb(wl_bins) * factor * 10 ** (- 2 / 5 * mag / u.mag) # / 1.195 * 1.16 # scaling for AETC validation
else:
sfd = bb(wl_bins)
# Initialize super class
super().__init__(SpectralQty(wl_bins, sfd), wl_bins)
@staticmethod
@u.quantity_input(temp=[u.Kelvin, u.Celsius])
def __rayleigh_jeans_factory(temp: u.Quantity):
"""
Create a lambda function for the Rayleigh-Jeans law
Parameters
----------
temp : u.Quantity
The temperature in Kelvins
Returns
-------
res : lambda
A lambda function for the Rayleigh-Jeans law with the variable lambda wavelength
"""
return lambda wl: (2 * c * k_B * temp / wl ** 4 / u.sr).to(u.W / (u.m ** 2 * u.nm * u.sr))
[docs] @staticmethod
def check_config(conf: Entry) -> Union[None, str]:
"""
Check the configuration for this class
Parameters
----------
conf : Entry
The configuration entry to be checked.
Returns
-------
mes : Union[None, str]
The error message of the check. This will be None if the check was successful.
"""
mes = conf.check_quantity("temp", u.K)
if mes is not None:
return mes
if hasattr(conf, "mag"):
mes = conf.check_quantity("mag", u.mag)
if mes is not None:
mes = conf.check_quantity("mag", u.mag / u.sr)
if mes is not None:
return mes
mes = conf.check_selection("band", ["U", "B", "V", "R", "I", "J", "H", "K", "L", "M", "N"])
if mes is not None:
return mes
if hasattr(conf, "law"):
mes = conf.check_selection("law", ["Planck", "RJ"])
if mes is not None:
return mes